Specific heat capacity is the slope (derivative) of the internal energy due to random motion of atoms in a sample as a function of temperature, normalized by dividing by the mass of the sample. Because the internal energy curve is normally almost linear, it can by approximated by measuring the heat required to raise the temperature of 1 kg of a substance by 1°C (or one Kelvin). The SI units of measurement for this are J·kg-1·K-1.

Factors that influence heat capacity measurements:

The temperature of the substance. For example, measuring the heat capacity of water produces different results if you start at 20°C, or 60°C.